The Labor Department, responding to complaints from organized labor and Fairfax County supervisors, announced yesterday that it is assigning six additional safety inspectors to construction sites in the county.

David Rhone, regional administrator of Labor's Occupational Health and Safety Administration (OSHA), said in letters to the county that the extra inspectors will augment, the three inspector's assigned to Northern Virginia by the state.

The state AFL-CIO, the Oil, Chemical and Atomic Workers Union and the Fairfax supervisors have petitioned OSHA to withdraw its approval of the Virginia inspection program, citing 15 construction deaths in the Washington suburbs in the last two years as an indication that the state program is inadequate.

Eula Bingham, assistant secretary of Labor for OSHA, in a letter to Gov. John N. Dalton, announced that OSHA will conduct informal hearings next month at four yet unselected locations in the state on the petitions.

Rhone said his action, effective Jan. 14, is an interim measure, aimed at bolstering inspections while OSHA completes a "comprehensive review" of the state-operated program.

Robert Beard Jr., director of the Virginia Department of Labor and industry, said the Virginia program, one of about 25 conducted by state governments with OSHA's approval, has resulted in an accident rate below the national average, and below that in Washington, where OSHA conducts inspections.

Beard said that the three inspectors assigned to Northern Virginia, out of a total of 16 checking construction sites in the state, is in proportion to the number of construction workers in the area, and in line with criteria recommended by OSHA.

"If there aren't enough inspectors in Fairfax, there also aren't enough in Richmond, Norfolk and elsewhere." Beard said yesterday. Beard said that the state reduced the number of construction site inspectors from 20 to 16 after OSHA, as part of its monitoring, suggested last year that state agents were making "too many inspections."

Rhone said that OSHA is anxious to explore the possibility, raised by Fairfax supervisors, of the county -- rather than the state -- providing building inspectors as OSHA compliance officers.

Fairfax Board Chairman John F. Herrity, the only supervisor who does not want to bypass the state completely in the inspection program, said yesterday that although he is "not enthused" about the idea of additional federal inspectors in the county his main concern is getting additional, well-trained inspectors at work at the more than 1,000 construction sites in the county.

Paul G. Edwards, a spokesman for Gov. Dalton, said OSHA's primary complaint, as outlined in the three-page letter from Bingham, is with the system of reviewing penalties assessed by the state's inspectors.

"OSHA made no issue of the adequacy of the inspection program or the state's safety records," said Edwards.